Bindings generator: Lazy loading of Qt bindings

Currently the bindings are loaded as "monolithic" libs, e.g. all of QtGui bindings in one library. It would be nice if (groups of) classes were only loaded on demand.
Another possibility is to split e.g. the QtGui typesystem into sub-packages; qt.gui.graphicsview, qt.gui.widgets and so on. Then you could explicitly import only the sub-packages that you want to use.